DVD recorder won't copy onto DVD R disks but will copy to DVD-R disks. Why?

DVD-R disks are the most common in use today and that's why it'll record -R disks. The older recorders didn't have the software embedded in them to record on an R disk, but the newer generation machines usually will. Without going into a lot of techno-babble,the R was a positive recording system and the -R was a negative recording system. Most commercial movies you buy are -R disks as well, and since my computer will record both, I choose the -R disks because I'm relatively sure they'll play on any DVD player.